Databases are computerized information storage and retrieval systems. A Relational Database Management System (RDBMS) is a database management system (DBMS) which uses relational techniques for storing and retrieving data. Relational databases are organized into tables which consist of rows and columns of data. The rows are formally called tuples or records. A database will typically have many tables and each table will typically have multiple tuples and multiple columns. The tables are typically stored on direct access storage devices (DASD), such as magnetic or optical disk drives for semi-permanent storage. Data stored in a database is selectively retrieved using a database query.
The data from a relational database is commonly retrieved using a Structured Query language (SQL) interface which is well known in the art. The SQL interface has been adopted as such by both the American Nationals Standard Organization (ANSI) and the International Standards Organization (ISO), and allows users to formulate relational operations on the tables interactively, in batch files, or embedded in host languages such as C, COBOL, etc. Operators are provided in SQL that allow the user to manipulate the data, wherein each operator operates on one or more tables and produces a new table as a result.
Query languages such as SQL require some expertise to write effectively. Since both users and applications heavily rely on query statements for retrieving information, tools have been developed to assist in the creation of query statements. These tools include a user interface for creating the initial query, and a query model for storing the components of the resulting query in a manner that enables their reconstruction. Once completed, the query is forwarded to the database management system for performing selective data access.
Query tools suffer from numerous shortcomings that have highlighted a need for a more useful and user-friendly query building tool. The assistance they provide is limited to basic query syntax, requiring manual input of more complex queries. Further, while existing query tools enable creation and modification of new query statements, they do not generally provide means for populating the interface and underlying model with existing query statements to enable modification of those statements.
Other shortcomings exist in the query models themselves. For example, existing models provide limited representation of complex query elements in formats that are not readily understandable to the developer. Moreover, they do not provide much flexibility for reconstructing the query and its subelements. In addition, they are often dependent upon the format of a particular user-interface and do not lend themselves well to use by graphical user interfaces of different formats.